Method and device for determining a drive force produced by an electric motor

Abstract

In order to determine a drive force (FAct) produced by an electric motor, the motor current (Ia) supplied to the electric motor ( 10 ) from a power supply source ( 32 ) is measured and a force is calculated from this; in addition, the motor voltage (UBat) applied to the electric motor ( 10 ) is measured, and drive force fluctuations which result from voltage fluctuations that occur during operation of the power supply source are compensated for, with at least one compensation force component being determined which is based on the measured motor voltage (UBat), including voltage fluctuations.

1. A mechanism for limiting the closing force of a component of a motor vehicle that is driven with the aid of an electric motor, comprising a device comprising force-determining means to be associated with an electric motor for determining a drive force produced by the electric motor during operation, the force-determining means being connected to motor current measuring means, wherein the force-determining means are connected moreover to means for measuring the motor voltage and have means for determining at least one additional force component used to compensate voltage fluctuations on the basis of the measured motor voltage including voltage fluctuations, and threshold value means for comparing the determined drive force of the electric motor, while taking account of the at least one compensation force component, with a specified threshold value, motor control means being connected to the threshold value means to reduce or switch off the motor output when the threshold value is reached. 
     
     
       2. The mechanism according to  claim 1 , wherein the force-determining means have low-pass filtering means for low-pass filtering the measured motor voltage, the low-pass filtered motor voltage being used when determining the compensation force component. 
     
     
       3. The mechanism according to  claim 2 , comprising means for forming the difference between the low-pass filtered motor voltage and the measured motor voltage, the force-determining means being constructed to determine a compensation force component from this difference to compensate forces on the basis of dynamic voltage fluctuations. 
     
     
       4. The mechanism according to  claim 3 , comprising multiplying module for multiplying the difference by a predetermined proportionality factor to calculate the compensation force component. 
     
     
       5. The mechanism according to  claim 1 , comprising means for forming the voltage difference between a maximum motor voltage and the low-pass filtered motor voltage, the force-determining means being constructed to determine a compensation force component from this voltage difference to compensate forces on the basis of static voltage fluctuations. 
     
     
       6. The mechanism according to  claim 5 , comprising a multiplying module for multiplying the difference by a predetermined proportionality factor to calculate the compensation force component. 
     
     
       7. A method for determining a drive force produced by a rotating electric motor, comprising the steps of:
 Measuring the motor current supplied to the electric motor from a power supply source; 
 Calculating a force from the measured motor current; 
 Measuring the motor voltage applied to the electric motor; and 
 Compensating drive force fluctuations which result from voltage fluctuations that occur during operation of the power supply source, wherein at least one compensation force component being determined which is based on the measured motor voltage including voltage fluctuations; 
 wherein the measured motor voltage is low-pass filtered and is used as the filtered motor voltage for determining the compensation force component; 
 wherein to compensate dynamic voltage fluctuations the difference between the filtered motor voltage and the measured motor voltage is formed and the associated dynamic compensation force component is calculated from this difference. 
 
     
     
       8. A method according to  claim 7 , wherein the dynamic compensation force component is calculated by multiplying the difference by a pre-determined proportionality factor. 
     
     
       9. A method for determining a drive force produced by a rotating electric motor, comprising the steps of:
 Measuring the motor current supplied to the electric motor from a power supply source; 
 Calculating a force from the measured motor current; 
 Measuring the motor voltage applied to the electric motor; and 
 Compensating drive force fluctuations which result from voltage fluctuations that occur during operation of the power supply source, wherein at least one compensation force component being determined which is based on the measured motor voltage including voltage fluctuations; 
 wherein the measured motor voltage is low-pass filtered and is used as the filtered motor voltage for determining the compensation force component; 
 wherein to compensate static voltage fluctuations the voltage difference between a maximum motor voltage and the filtered motor voltage is formed and the associated static compensation force component is calculated from the voltage difference. 
 
     
     
       10. A method according to  claim 9 , wherein the static compensation force component is calculated by multiplying the voltage difference by a predetermined proportionality factor. 
     
     
       11. A device comprising:
 force-determining means to be associated with an electric motor for determining a drive force produced by the electric motor during operation; 
 the force-determining means connected to motor current measuring means; 
 wherein the force-determining means are connected to means for measuring the motor voltage and include means for determining at least one additional force component used to compensate voltage fluctuations on the basis of the measured motor voltage including voltage fluctuations; 
 wherein the force-determining means include low-pass filtering means for low-pass filtering the measured motor voltage; 
 the low-pass filtered motor voltage being used when determining the compensation force component; and 
 means for forming the difference between the low-pass filtered motor voltage and the measured motor voltage; 
 the force-determining means constructed to determine a compensation force component from this difference to compensate forces on the basis of dynamic voltage fluctuations. 
 
     
     
       12. A device according to  claim 11 , further comprising a multiplying module for multiplying the difference by a predetermined proportionality factor to calculate the compensation force component. 
     
     
       13. A device comprising:
 force-determining means to be associated with an electric motor for determining a drive force produced by the electric motor during operation; 
 the force-determining means connected to motor current measuring means; 
 wherein the force-determining means are connected to means for measuring the motor voltage and include means for determining at least one additional force component used to compensate voltage fluctuations on the basis of the measured motor voltage including voltage fluctuations; 
 wherein the force-determining means include low-pass filtering means for low-pass filtering the measured motor voltage; 
 the low-pass filtered motor voltage being used when determining the compensation force component; and 
 means for forming the voltage difference between a maximum motor voltage and the low-pass filtered motor voltage; 
 the force-determining means being constructed to determine a compensation force component from this voltage difference to compensate forces on the basis of static voltage fluctuations. 
 
     
     
       14. A device according to  claim 13 , further comprising a multiplying module for multiplying the difference by a predetermined proportionality factor to calculate the compensation force component.